1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt with a plurality of ribs extending lengthwise of the belt.
2. Background Art
Power transmission belts are used on a wide range of vehicles in many different environments. As an example, power transmission belts are used to drive auxiliary components such as air compressors, alternators, or the like, on such vehicles. Over the years, the performance expectations for such belts have increased.
There is a growing emphasis on minimizing noise generation during operation of such vehicles. Efforts have been made to eliminate, to the extent possible, all noise other than that generated by the engine of the vehicle itself, during operation. To achieve this end, measures have been taken to minimize sound generation caused by the interaction between power transmission belts and complementary pulleys that drive and/or are driven by such belts.
Sound tends to generate when belts slip relative to cooperating pulleys, as may be caused by variations in the rotational speed of the engine and/or operation under high load conditions. Additionally, noise generates as belt ribs wear during normal operation, as an incident of which the ribs tend to adhere to the bottom of cooperating grooves, particularly with a V-ribbed belt construction.
Noise also tends to generate in systems wherein there is misalignment of system pulleys that causes the belts to twist and/or skew as they move in their respective paths. Sound generates based upon disproportional loading. All of these conditions may generate noise that is audible to occupants of the vehicles.
Rubber belts are generally required to transmit relatively large forces not only under dry conditions, but also in humid conditions and in conditions wherein water, as in the form of rain, is in contact with the belts and pulleys. As one example, with an engine operating, water entering the engine compartment in rainy weather tends to migrate into gaps between the belts and cooperating pulleys. As a result, the slip rate of the belts increases, which compromises their performance by reducing their ability to transmit forces. This condition also is responsible for noise generation.
To address the above problems, it is known in the art to incorporate into the rubber, defining ribs of a V-ribbed belt, cotton short fibers, together with nylon short fibers having an intermediate elasticity modulus between the elasticity modulus of the belt body rubber and that of the cotton short fibers. This construction is disclosed in JP-A-2003-202055.
In this construction, the cotton and nylon short fibers suppress the rapid slip phenomenon that tends to generate unwanted noise during operation.
To effectively control the slip phenomenon and noise generation, the cotton and nylon short fibers must be exposed at the surfaces of the belt, such as those on a V-ribbed belt, that engage cooperating pulley surfaces. To accomplish this, the fibers are fully embedded in the belt rubber during formation. The fibers are oriented laterally in the ribs. To form the ribs, the rubber layer in which the fibers are embedded is cut. This results in potentially relatively high manufacturing costs and also produces rubber waste that must be handled after the belt formation.
With this construction, most of the short fibers in the ribs are fully embedded in the rib rubber. The portion of the fibers exposed at the pulley-engaging surfaces is relatively small compared with the overall blended quantity of the short fibers within the rubber. As a result, the exposed fiber portions may not effectively suppress slippage and avoid unwanted sound emission.
To address this concern, the amount of short fibers within the rubber may be increased. However, by so doing, the flexibility of the belt may be significantly compromised. Alternatively, the degree of exposure of the embedded fibers may be increased by deforming the projecting portions thereof, as through a polishing process. As a practical matter, the deformation of the short fibers caused by the polishing is relatively insignificant. It is practically impossible to significantly increase the amount of exposure of the short fibers by this process, or other processes, without detrimentally increasing the density of fibers within the rubber composition.
By increasing the quantity of fibers, aside from decreasing belt flexibility, the lifetime of the belt may be significantly reduced due to the non-uniform dispersal of the short fibers in the rubber. This condition commonly occurs with a greater density of the fibers. Thus, these prior art attempts to suppress slippage and unwanted noise are lacking in terms of their overall effectiveness.
The industry continues to seek out designs that adequately address the above issues without compromising other performance aspects of the belt.